1. Field of the Invention
This invention relates to compositions which are curable by exposure to ambient moisture, and more particularly to such compositions which comprise a blend of a silyl group containing resin and a curing catalyst.
2. Description of the Prior Art
There are known in the prior art various silicon compounds containing a silicon atom attached to a hydrolyzable group. These compounds have good adhesion to inorganic substances because of the action of their hydrolyzable silyl group. Also, there is cross linking at ambient temperatures upon exposure to moisture, especially atmospheric moisture to form cured products having excellent durability. These compounds are thus extensively employed as paints, coating agents, adhesives, sealants, silane coupling agents, and the like.
However, when these silicon compounds containing a silicon atom attached to a hydrolyzable group are used without a curing catalyst, they are slow in curing speed at room temperature, or at a relatively moderately elevated temperature. Thus, when a coating of such compound is required to be cured at a high rate, a high degree of heating at a high temperature is required. Accordingly, in such an instance, an enormous amount of energy is needed.
To cure this deficiency, it has been suggested to use a curing catalyst incorporated into the curable composition, immediately prior to use, to thereby enhance the curing speed of the coating at a relatively low temperature. However, disadvantageously, once a curing catalyst is added to such a composition, it cannot be stored for any length of time because the composition will cure in a short length of time. Thus, when a part of the composition, such as for example a paint composed of such composition, has been used, the unused remainder is essentially wasted. Such curable compositions are generally called a two-pack type of curable composition.
On the other hand, a curable composition may include therein a curable catalyst, in which case, no other composition or catalyst need be added immediately prior to use. This type of curable composition is called a one-pack type of curable composition. One known as a one-pack type of composition comprises a blend of a curing catalyst and a silicon compound having a backbone of hydrolyzable silyl group and having siloxane bonds. This prior one-pack type of composition has been found to have some deficiencies, such as non-optimal hardness after during, insufficiently good storage stability, only average workability and weather resistance.
Accordingly, there is still a need in the prior art for a one-pack type of curable composition which has excellent storage stability, high hardness of the cured surface, excellent workability and weather resistance.